Electric discharge lamp



March 1950 R. L. BREADNER ET AL 2,501,375

ELECTRIC DISCHARGE LAMP Filed Feb. 25, 1946 Inven't'ors Eobert' Leonard Breadner',

Henrg Graingr Jenkins,

Charles Henry Simms,

Then" A t'tovneg Patented Mar. 21, 1950 ELECTRIC DISCHARGE LAMP Robert Leonard 'Breadner,

Kenton, Henry Grainger Jenkins, Pinner, and Charles Henry Simms, Twickenham, England, assignors to General Electric Company, a corporation of New York Application February 25, 1946, Serial No. 650,066 In Great Britain December 21, 1944 Section 1, Public Law 690, August 8,1948 Patent eipires December 21, 1964 3 Claims. (01. 176-122) The present invention relates to electric discharge lamps having long positive-column discharge paths and having their envelopes coated internally with fluorescent powder. The invention is applicable both to cold cathode lamps of the kind usually operated from high voltage and and also to hot cathode lamps of the kind frequently operated from ordinary supplyvoltages. The invention is therefore applicable to hot cathode lamps, in which the discharge passes through mercury vapour usually admixed with a few millimetres pressure of a rare gas such as argon, the discharge causing the powder coating on the envelope to fiuoresce. Such lamps are now of great importance as light sources.

The dimensions of these fluorescent lamps, which are usually but not necessarily of circular cross-section, may vary, for example, from a few inches to several feet in length and from to 2" in mean diameter. They are usually made by mass production methods and are, therefore, generally straight lengths of tubing. Other shapes, such as grids, spirals, etc., have often been proposed but such shapes do not lend themselves readily to mass production methods and can be obtained, in general, only by manipulation :by skilled craftsmen. ihe operation becomes progressively more dimcult to perform as the diameter of the tubing is increased, and as the radius of curvature is decreased.

The simple straight tube has several practical disadvantages. As it may be several feet in length, it obviously requires considerable care in handling to avoid mechanical breakage.

Furthermore, since the electrodes are situated at opposite ends of the tube, a straight tube will require two widely separated external contacts or caps which may need to be very accurately spaced apart to fit into a housing with pre-set sockets for the supply of electric power. Also large linear sources are dimcult to deal with optically and where a fitting is used this is large and costly in relation to the wattage of the lamp. For these reasons low pressure fluorescent lamps have been virtually ruled out for street lighting where the excellent spectral characteristics of their light might be used to great advantage.

The invention is concerned with discharge lamps of the type in which compactness is secured by giving the passage, through which the discharge passes between two electrodes located in said passage, a. spiral shape, in which the discharge passage is a channel formed between two vitreous components, one or both of the components having one or more upstanding ridges 66 which separate adjacent parts of the discharge passage from one another, in which the walls-of the discharge passage are coated with a luminescent material-and in which the discharge passage is provided with a gas and/0r vapour filling.

The term spiral is intended to include a helix and other intermediate shapes in which the centre line of the convolutions lies in a dished surface.

Lamps of the type described have already been proposed but for'various reasons have not been successful in providing an eflicient lamp of good appearance which is adapted to quantity production methods.

It is the object of the present invention to overcome the defects of known lamps and to this end makes use of a number of features, some or all of which are or may be inthemselves known in lamps of the type in question, but which have not hitherto been used in combination.

Thus it has been found essential for quantity production and avoidance of cracks that the vitreous material of the envelope should be reintively thin, that it should be in smooth curves, and that its general shape should be that of a surface of revolution. The avoidance of sharp angles in the cross-section of the discharge path is also desirable if the fluorescent powder is to be applied uniformly. It h necessary that the discharge path should be; sealed along its length tov glass member in the general form of a surface of revolution located within an outer blown glass member in the general form of a surface of revolution, one or both of said members having a. spiral groove formed in its surface during the blowing operation, whereby the grooved surface has a shape such that its section by a plane containing the axis of the members is wave-like or rippled, and the minimum radius of curvature of the surface of the waves or ripples at any point is at least equal to the maximum thickness of the glass at points away from the regions of sealing, the two members being sealed together along the crests of the waves or ripples, and tubulations, forming or connected to chambers containing the said electrodes, being connected to or near the ends of said discharge passage.

The lower limit given for the ratio or the radius of curvature of the waves or ripples to the thickness of the glass is not. in astrict sense, critical;

goons-re but a lower ratio than one-to-one has been found liable to lead to manufacturing difllculties. It should also be understood, in regard to the foregoing statement, that the maximum thickness of the glass means the maximum thickness at any place (on the rippled portion) not sealed to the other member. At places at which one member is sealed to the other, the "thickness to be attributed to either ceases to be definite. Generally, it is convenient that the smallest radius of the glass at the trough of a ripple (i. e. at the smallest diameter at the inner member, when the inner member is rippled, and at the largest diameter of the outer member, when theouter member is rippled), shall be at least five times the thickness at that point.

The invention will be described by way of example with reference to the accompanying drawing in which Figs. 1, 2 andg3 show in sectional elevation three steps in the manufacture of a lamp according to the invention, and

Fig. 4 is a view, also in sectional elevation, of a modified form of lamp according to the invention.

Referring to Fig. 1, an inner component I is blown into a mould to the shape shown. It will be seen that it has the general shape of a cylinder with a domed or hemispherical end and the mould is so shaped as to give the surface of the inner member a wave-like or rippled form. The crests ll of the waves or ripples are separated by troughs I2 and extend around the member in the form of a spiral, in this example approximately a helix. The inner member is next provided with tubulations l3 and M as shown in Fig. 2, these tubulations connecting with the two ends of the spiral groove or trough I2. The sealing of the tubes l3 and H to the inner member may be performed in any known or suitable manner, for example by the method disclosed in British patent specification No. 534,952.

As shown in Fig. 2, the inner member is then placed within an outer member l5 which is also blown into a mould to the same general shape as the inner member but has a plain, as distinct from a wave-like, surface. The inner member is arranged to be an easy fit within the outer member.

The two components and i5 are then sealed together along the whole length of the crests it thus forming a discharge passage of approxi mately helical shape which is sealed along its whole length between the tubulations l3 and [4. The sealing together may be performed by collapsing the outer component on to the crests H of the inner component in or by local and progressive melting with a small flame along the crests H. In the latter method, the continuous travel of the flame along the crests can be con trolled by well-known mechanical means. Other methods of performing the sealing of the two components together will be obvious to those skilled in the art, for example the components may be suitably heated and rolled or tooled into contact.

The result of the sealing operation is shown in Fig. 3. The envelope is then coated internally with luminescent powder, for example by dusting using the method described in British patent specifications Nos. 421,932 and 460,756. Electrodes l6 and I? are then sealed through pinches formed in the lower ends of the tubulations l3 and I4, the envelope is evacuated, pro- 4 vided with a suitable gas and/or vapour filling, and sealed 05.

It is arranged that the minimum radius of curvature of the surface of the inner member In, which is usually at the crests I I, is at least equal to the maximum thickness of the glass at any placeon the rippled surface not sealed to the outer'member. Thus in Fig. 3 considering the part of the discharge passage marked i8, the radius of curvature is a minimum at about the points I9 and this radius of curvature is made at least equal to the maximum thickness of the glass surrounding the passage excepting in the regions II where the two components are sealed together and the thickness is not definite. Moreover the radius of curvature at the troughs I2 is preferably made at least five times the minimum thickness of the glass at any point away from the regions I i.

In an alternative construction shown in Fig. 4 the outer member 20 is provided with a spiral groove having troughs 2i and ridges 22. The inner member 23 is plain and as before is provided with tubulations I 3 and I4. Fig. 4 corresponds to Fig. 2 and the subsequent operations described with reference to Fig. 3 may be performed on the embodiment of Fig. 4.

In this case the minimum radius of curvature of the waves or ripples is usually. as before, at the crests 22 and this minimum radius is again made at least equal to the maximum thickness of the glass wall at any point away from the crests 22 where sealing takes place. The minimum radius of curvature at the troughs 2i is also preferably made five or more times the maximum thickness of the glass wall at any point other than in the regions of sealing 22.

It may be noted that in Figs. 1 to 3 the troughs are located at approximately the smallest diameter parts of the inner member 10, whereas in Fig. 4 they are located at approximately the largest diameter parts of the outer member 20.

In the examples illustrated both members have the general form of cylinders with domed or hemi-spherical ends. Other shapes may, however, be employed so long as the general form is that of a surface of revolution.

We claim:

1. An electric discharge lamp comprising a bulb composed of an inner and an outer glass member in nested relationship and in the general shape of coaxial cylinders closed at one end by domed portions, at least one of said members having a spiral groove in its surface extending to the tip of the domed portion thereof whereby the grooved surface has a shape such that its section by a plane containing the axis of the members is wave-like, said two members being hermetically sealed together along the crests of said waves and thereby forming a discharge passage of spiral shape therebetween, a gaseous filling in said discharge passage, electrode chambers extendin interiorly of the bulb from the open end thereof to the ends of said passage re spectively adjacent the said open end of the bulb and at the tip of the closed end thereof, and an electrode in each of said chambers.

2. An electric discharge lamp comprising a bulb composed of an inner and an outer glass member each in the general shape of a surface of revolution hermetically sealed together to form a discharge chamber, at least one of said members having a spiral groove in its surface, whereby the grooved surface has a shape such that its section by a plane containing the axis of the members is wave-like, and the minimum I radius of curvature of the surface of the waves at any point is at least 5 times the maximum thickness of the glass at points away from the regions of sealing, said two members being sealed together along the crests of said waves and there by forming a discharge passage of spiral shape, a luminescent material upon the walls of said passage, a gaseous filling in said discharge passage, an electrode chamber sealed to each end of said passage, and an electrode in each of said chambers.

3. An electric discharge lamp comprising a bulb composed 01' an inner and an outer glass member in the general shape of coaxial cylinders closed at one end by domed portions and hermetically sealed together to form a discharge chamber, at least one of said members having a spiral groove in its surface, whereby the grooved surface has a shape such that its section by a plane containing the axis of the members is wave-like, said two members being sealed together along the crests of said waves and thereby forming a discharge passage of spiral shape, a luminescent material upon the walls of said passage, a gaseous filling in said discharge passage, an electrode chamber sealed to each end of said passage, and an electrode in each of said chambers.

ROBERT LEONARD BREADNER.

HENRY GRAINGER JENKINS.

CHARLES HENRY SIMMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Mahlck Apr. 13, 1943 

